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Cognitive Neuroscience Lecture 11: Language Lecture 1
L11: Language Guest Lecture: Language in the brain—from fundamentals to applications Language in the brain Language – A formal system for relating signals and meanings • Language comprehension: signal à meaning • Language production: meaning à signal Language is distinct from speech, thought or communication - Language different from speech: o Parrots & computers produce speech but not language o Language communicated via speech or writing - Language different from thought o Language verbalizes thought o Bi-linguals express same thoughts in different languages o Brain injury may damage language but you can still think - Language is different from communication o Body language, math Language Knowledge - Innate o Critical periods: exposure during limited time in development (adolescence) is critical for normal devàprocess with its own “clock” § Children not exposed before adolescence fail to acquire it later § 2nd language harder when learned after adolescence o Genetically linked to language deficits § Developmental language disorders not due to evident neural injury - 2 sources of our language knowledge o Genetic blueprint (innate neural/cognitive machinery) § Explains aspects of language that are the same across languages (universal grammar) o Learning § Allows us to learn characteristics of specific language one is exposed to · Explains aspects of language that are different across languages - Language is productive o Understand and produce infinite number of sentences never produced or heard before o How? § System of rules (grammar) for combining elements (words) o Rule system § Allows for sentences to be understood and produced similarly across ppl § Everyone has same definition for gramattical vs non - Language is multi-componential o Multiple components specialized for processing different aspects of language knowledge § Semantics: word meanings § Syntax: word ordering § Phonology: word sounds o Components used in comprehension and production of language o Patterns of language ability and disability subsequent to neural injury o Aphasia: language impairment o Cases exhibit full range of double dissoc § phonology vs semantics § syntax vs semantics Phonology: knowledge of language sounds - phonemes: smallest unit sound that distinguishes one word from another in a given language o po't'/po'd' - Phonological words (morphemes): combinations of sounds that comprise meaningful units o Giraffe-s à2 o Un-happi-nessà3 - Semantics: word meaning o Semantics: our knowledge of the meanings of words that allows us to use and understand them appropriately § More complex than dictionary def o Sweep vs. swept - Syntax: rules o Knowledge of how words can be combined in ordered to express meaning o English = SVO Language network: overview - Fmri conditions: spoken and written stories vs. scrambled spoken/written stim - Perisylvian language areas o Frontal lobe: inferior frontal gyrus o Temporal lobe: superior and middle temporal gyri o Parietal lobe: supra-marginal and angular gyri o Broca’s area: BA 44/45 o Wernicke’s area: BA 22 o - Language Lateralization: is it limited to left hem? o Neuroanatomical asymmetries § Planum temporale: auditory processing region within Sylvian fissure § LH larger than RH in most right-handers (starts at 31st week of gestation) § o How are the language functions distributed across hemispheres? o How can we find out? § Isolate the hemis § WADA § Commisurotomy · Separate hemis by cutting corpus callosum · Treats intractable epilepsy · Test hemis separately with 1 vis field presentation § Hemispherectomy · Surgical treatment for tumors and rasmussen’s syndrome · Affects RH or LH - Right Hemisphere Language? o Limited and redundant (not necessary) o Hemi differences between comprehension and production § Left: production § Right: comprehension o Good recovery in response to early damage § Early damage shows right hemi’s latent language capacities o Difference in neuroimaging and lesion studies in terms of right hemi involvement? § Lesion studies reveal necessary neural substrates (but not sufficient) Phonological aspects of language processing: Ventral: Comprehension: AudàSTGàMTG/ITGàATL Dorsal: Production: STGàSptàSMGàIFG+PM Ventral stream damage - Intact environmental sound identification, visual recognition, semantic knowledge - Impaired speech comprehension (discrim, ID, repetition of word he just heard, comprehension) o Phoneme ID difficult o Phonological word id difficult Dorsal stream damage - Trouble with phon. Word selection, phoneme selection, motor planning Evidence from defecits affecting semantic categories - Lesion locations associated with selective deficits in naming words from specific categories (people, animals, tools) o Left middle and inferior temporal gyri - Evidence from voxel based morphometry o Semantic dementia § Degenerative disease: loss of understanding of word meanings § Cortical atrophy o Mummery et al: § VBM measures cortical thickness at each voxel · Atrophy left lateralized in anterior temporal lobe (temporal pole) Using ERP to examine syntactic processing - How could we isolate syntactic processing in neuroimaging/disruption studies? o Grammatical vs. ungrammatical sentences o More complex vs. less complex o Syntax but no semantics (jabberwocky) - Left anterior negativity characteristic ERP response after syntactic violation - Distribution over time and electrodes of differences in brain response to grammatical vs. ungrammatical word o LAN at 450-500ms o Early and later ERP identified at left anterior electrodes (left frontal cortex) fMRI: sentences with and without meaning - Jabberwocky compared to just lists of nonword - Left IFG consistently associated w/ lesions affecting syntactic processing and activation studies - Other perisylvian language areas also associated w/ syntactic processing - Conclusions? o H1: Syntactic processing distributed o H2: we have not yet figured out how to isolate syntax from other aspects of language processing Language network - Basic language processes - Neural substrates - Methods and results